This application relates generally to tracking objects via wireless signals and more specifically to tracking objects using radio frequency identification (“RFID”) techniques. In its most basic form, an RFID system uses tags or labels attached to the objects to be identified or tracked. Two-way radio transmitter-receivers called interrogators or readers send a signal to the tag and read its response. RFID tags can be either passive, active or battery-assisted passive. An active tag has an on-board battery and periodically transmits its ID signal. A battery-assisted passive (BAP) tag has a small battery on board and is activated when in the presence of an RFID reader. A passive tag is cheaper and smaller because it has no battery; instead, the tag uses the radio energy transmitted by the reader. The basic operation of the RFID Reader involves the reader generating a radio frequency signal, having the signal “activate” the RFID tags, and the reader receiving the unique reflected signals from the RFID tags.
Although the basic operation of RFID systems are well known in the art, the actual environment in which a system must operate can make reliable and accurate detection of RFID tags technically challenging. For example, determining whether a RFID tag has moved a comparatively short distance (i.e., from one room to another room in the same building) may be uncertain because the RFID reader can detect the tag in both rooms. Also, many objects in the environment may be highly reflective of radio signals, resulting in many “echoes” of both the reader's signal and the tag's reflected signal. Moreover, the sheer number and close proximity of RFID tags in many applications creates an extremely noisy and complex signal environment. Techniques which help resolve the above issues and other problems in RFID systems are always a welcome addition to the art.